The invention relates to a method for the manufacture of components made of steel for use under heavy stress, load and/or wear, such as rolling bearing elements.
Normally, components such as rolling bearing elements are manufactured from a steel with 1% by weight C. The steel is heated to a temperature of about 1100.degree. C. and is given its form in a hot forming step. It is then allowed to cool in air. Next, the steel is soft annealed, then soft machined, thereafter hardened by quenching from 850.degree. C. in oil or salt, and then ground and surface finished. After this, the element can be assembled with other elements. The most costly part of this manufacturing method is the grinding step. Even if the components have their intended final dimensions and tolerances after the soft machining step, the hardening step will cause distortion of the component, and a large share of the total costs can be incurred in the grinding step.
Further, the components are heated to high temperatures at least twice after the hot forming treatment resulting in a high energy consumption. The process is also time consuming, and because of the quenching step, this known process also creates environmental problems and fire hazards.
SE-C-467 829 discloses a method of producing components from steel with an eutectoidal composition, according to which a blank is formed at a temperature just above the Al temperature of the steel to a shape at least approximately having the final dimensions, whereupon the hot formed component is hardened directly from the hot forming temperature. According to the preferred embodiment, no soft annealing step is performed before the heating to the hot forming temperature. The hot forming is a semi-hot forming process, which is performed at 750.degree.-850.degree. C., and the component is quenched in oil directly from the hot forming temperature, resulting in a sufficient hardness.
An important advantage with this process is that the time consuming, costly and complicated soft annealing process can be deleted, but still there is a need for further improvement of this process.